Which mathematical model is most commonly used by major e-commerce platforms to implement their 'Customers Who Bought This Also Bought' recommendation systems?

Retail operations have been revolutionized by advanced mathematical models that help predict customer behavior, optimize inventory, and maximize sales. Behind these powerful tools are specific mathematical concepts that drive big data analytics in the retail sector. Test your knowledge about how mathematics is applied in modern retail operations and customer insight analysis!

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Markov Chain Monte Carlo (MCMC)
Collaborative Filtering with Matrix Factorization
Bayesian Structural Time Series (BSTS)
Gradient Boosted Decision Trees (GBDT)